Several parents of schoolgirls kidnapped by Boko Haram in Nigeria have been able to identify their daughters in a video released by the militants, according to local officials.

The authorities have been showing the film to the families but efforts to establish which girls are among the 130 in the footage have been hampered by electricity supply problems in Chibok, Borno state, where they were seized more than four weeks ago.

The authorities have been showing the film to the families but efforts to establish which girls are among the 130 in the footage have been hampered by electricity supply problems in Chibok, Borno state, where they were seized more than four weeks ago.

In the video, Boko Haram claimed the girls, who were shown apparently praying, had converted to Islam. The co-ordinator of the Bring Back Our Girls campaign, which has helped drive international pressure for action through social media and global street protests, said at least three parents had recognised their daughters.

"(Borno) Governor (Kashim) Shettima has now organised a screening in (the state capital) Maiduguri with audio and is bringing parents from Chibok to try to identify more girls," Hadiza Bala Usman said from the Nigerian capital Abuja. Dumoma Mpur, chairman of the local parent-teachers association, said: "The video got parents apprehensive again after watching it, but the various steps taken by the governments and the coming of the foreign troops is boosting our spirit."

Meanwhile, former British prime minister Gordon Brown urged Boko Haram to release image so of the 276 schoolgirls they are believed to be holding in order to prove they are still alive. Mr Brown, who has been visiting Nigeria in his role as United Nations special envoy for global education, said the snatching of the girls from their school in the northeast of the country was "every parent's nightmare".

Image:The kidnap of the schoolgirls has sparked international condemnation

"If we can track down and locate the girls and then release them, that would be a blow to the efforts of Boko Haram, who have killed almost 5,000 people in the last few years," he added. However, a civil rights activist and former Boko Haram mediator called on the Nigerian government to open talks with the militants or risk the girls being killed.

Shehu Sani told Sky News: "Negotiation is the best way to get the girls out. We cannot contemplate using force because it will end up with their lives at risk. "No doubt, any attempt to use force to rescue the girls and the insurgent group will kill these girls."

Video:British General On Nigeria Kidnaps

The group are offering to exchange the girls for prisoners, although this has been rejected by the Nigerian government. The United States is flying manned surveillance missions over the region to assist the hunt for the schoolgirls and Britain has indicated it could also provide air support, including drones.

The former head of Britain's Special Forces has said military intervention may be necessary, although he admitted it would not be without risk. Major General Jonathan Shaw told Sky News: "One of the problems of the press coverage of special forces operations over the years has been that they have special forces magic dust, there is no such thing, this is just advanced infantry tactics and sometimes they succeed and sometimes things go wrong.

"Sometimes you can do a neat surgical raid, and sometimes it has to be rather large and messy, so in our own minds I don't think we should have any expectation of any clean clinical finish to this." A British team including counter-terrorism and intelligence experts in Nigeria has held talks with counterparts and political leaders as well as a group representing the families of the girls.